Fantastic Four: Age, Spinal Cord Stimulator Waveform, Pain Localization and History of Spine Surgery Influence the Odds of Successful Spinal Cord Stimulator Trial

BACKGROUND

There is a dearth in our understanding of the factors that are predictive of successful spinal cord stimulator (SCS) trials and eventual conversion to permanent implants. Knowledge of these factors is important for appropriate patient selection and treatment optimization.

OBJECTIVES

Although previous studies have explored factors predictive of trial success, few have examined the role of waveform in trial outcomes. This study sought to establish the relationship of neuraxial waveform and related measures to trial outcomes.

STUDY DESIGN

This study used a retrospective chart review design.

METHODS

Data were retrospectively collected on 174 patients undergoing SCS trials upon institutional review board approval of the study protocol. Indications for SCS were: complex regional pain syndrome, failed back surgery syndrome with radicular symptoms, peripheral neuropathy, and axial low back pain. Descriptive statistics and logistic regression analyses were used to assess the association of demographic and clinical variables with SCS trial outcomes.

RESULTS

The study population comprised 56% women, had a median age of 55 (interquartile range [IQR], 44-64), and 32 of 174 (18%) patients failed SCS trials. Individuals with successful trials (>= 50% pain relief) were significantly younger and had a median age of 54 years (IQR, 42-60) compared to those who failed SCS trials (median age 66 years; IQR, 50-76; P = .005). Adjusting for age, gender, number of leads, pain category, and diagnoses: surgical history (odds ratio [OR] = 4.4; 95% confidence interval [CI], 1.3-15.8) and paresthesia-based tonic-stimulation (OR = 10.3; 95% CI, 1.7-62.0), but not burst or high frequency, were significantly associated with successful trials. Of note, the number of leads (whether dual or single), pain duration, characteristics, and category (nociceptive vs neuropathic) were not significant factors. An interaction between surgical spine history and lower extremity pain was significantly associated with a positive trial (P = .005).

LIMITATIONS

This study was limited by its retrospective nature and focus on a patient population at a single major academic medical center.

CONCLUSIONS

Paresthesia-based tonic stimulation, age, and surgical history have significant effects on SCS trials. Prospective and randomized controlled studies may provide deeper insights regarding impact on costs and overall outcomes.IRB Approval #: 2018P002216.

KEY WORDS

Pain duration, pain location, spinal cord stimulator trial, stimulator waveform, surgical history.

Long-term efficacy of 1-1.2 kHz subthreshold spinal cord stimulation following failed traditional spinal cord stimulation: a retrospective case series

BACKGROUND AND OBJECTIVE

We investigated whether an effective long-term pain relief could be achieved using subthreshold 1-1.2 kHz spinal cord stimulation (SCS) among patients who were initially implanted with traditional paresthesia-based SCS but who failed to maintain an adequate pain relief.

METHODS

Retrospective chart review was conducted of patients' electronic records who underwent a trial of subthreshold 1-1.2 kHz SCS. One hundred and nine patients implanted and programmed at traditional paresthesia-based frequencies 40-90 Hz (low-frequency SCS) with unsatisfactory pain relief or unpleasant paresthesias were identified. Patients' settings were switched to 1-1.2 kHz and 60-210 µs, and variable amplitude adjusted to subthreshold. Pain scores and medication usage were collected. Complete data are presented on 95 patients.

RESULTS

Data were collected from 36 men and 59 women who were converted from above-threshold 40-90 Hz SCS to 1-1.2 kHz SCS, with a minimum follow-up of 12  months. Nearly a third (63/95 or 66.3%) of the subjects deemed 1-1.2 kHz SCS ineffective and returned to low-frequency SCS within 1 week after switch, and one-sixth (16/95 or 16.8%) of the subjects returned to low-frequency SCS within 1 month. Only 13 (13.7%) subjects continued using 1-1.2 kHz subthreshold SCS for 3 months or longer and 2.1% (2/95) of subjects continued using it at 12 months. A comparison of their pain scores and opioid use before and during the time we used 1-1.2 kHz SCS revealed no significant difference.

CONCLUSION

The results from our single center failed to show additional long-term clinical benefit of 1-1.2 kHz subthreshold SCS in patients with chronic pain failing traditional low-frequency SCS.

Recovery cycles of posterior root-muscle reflexes evoked by transcutaneous spinal cord stimulation and of the H reflex in individuals with intact and injured spinal cord

Posterior root-muscle (PRM) reflexes are short-latency spinal reflexes evoked by epidural or transcutaneous spinal cord stimulation (SCS) in clinical and physiological studies. PRM reflexes share key physiological characteristics with the H reflex elicited by electrical stimulation of large-diameter muscle spindle afferents in the tibial nerve. Here, we compared the H reflex and the PRM reflex of soleus in response to transcutaneous stimulation by studying their recovery cycles in ten neurologically intact volunteers and ten individuals with traumatic, chronic spinal cord injury (SCI). The recovery cycles of the reflexes, i.e., the time course of their excitability changes, were assessed by paired pulses with conditioning-test intervals of 20–5000 ms. Between the subject groups, no statistical difference was found for the recovery cycles of the H reflexes, yet those of the PRM reflexes differed significantly, with a striking suppression in the intact group. When comparing the reflex types, they did not differ in the SCI group, while the PRM reflexes were more strongly depressed in the intact group for durations characteristic for presynaptic inhibition. These differences may arise from the concomitant stimulation of several posterior roots containing afferent fibers of various lower extremity nerves by transcutaneous SCS, producing multi-source heteronymous presynaptic inhibition, and the collective dysfunction of inhibitory mechanisms after SCI contributing to spasticity. PRM-reflex recovery cycles additionally obtained for bilateral rectus femoris, biceps femoris, tibialis anterior, and soleus all demonstrated a stronger suppression in the intact group. Within both subject groups, the thigh muscles showed a stronger recovery than the lower leg muscles, which may reflect a characteristic difference in motor control of diverse muscles. Based on the substantial difference between intact and SCI individuals, PRM-reflex depression tested with paired pulses could become a sensitive measure for spasticity and motor recovery.

Effectiveness of "Transgrade" Epidural Technique for Dorsal Root Ganglion Stimulation. A Retrospective, Single-Center, Case Series for Chronic Focal Neuropathic Pain

BACKGROUND

The recent interest in targeting the dorsal root ganglion (DRG) has led to the development of new techniques of electrode placement. In this article, we describe a new "Transgrade" approach to the DRG, accessing the contralateral interlaminar space and steering the lead out the opposite foramen.

OBJECTIVES

The purpose of this study was to evaluate the Transgrade technique to the DRG in the management of focal neuropathic pain, predominately complex regional pain syndrome in terms of efficacy and safety.

STUDY DESIGN

A retrospective, observational review of all patients selected for DRG stimulation using the Transgrade technique to the DRG.

SETTING

Pain Management and Neuromodulation Centre, Guys and St. Thomas NHS Foundation Trust, London, United Kingdom.

METHODS

Data were taken from a hospital password-protected database. All patients were contacted by telephone for Numeric Rating Scale (NRS-11) score, Patient Global Impression of Change (PGIC) score, and complications. A patient responder was defined as having a PGIC score of 6 or 7, and a 2-point reduction from baseline NRS-11.

RESULTS

A total of 39 patients (46% women) with a mean age of 46 years (± 2) underwent a trial of DRG stimulation that resulted in an implantation rate of 82% (32 of 39). The responder rates, according to NRS-11 and PGIC results, were 87% (28 of 32) at 6 weeks and 66% (21 of 32) at a mean of 18 months (± 1.8) follow-up. Pocket pain was the most common complication, occurring in 7 of 32 (22%) patients, and the lead migration rate was 3 out of 57 leads placed (5.2%). A burst protocol was the favored method of stimulation in the majority of patients, 25 of 32 (78%).

LIMITATIONS

Retrospective nature of design, small sample size.

CONCLUSIONS

The Transgrade technique of placing DRG leads offers an alternative method that is safe and effective. New methods of stimulation to the DRG offer more choice and potentially better efficacy for patients with chronic neuropathic pain.

KEY WORDS

Neuromodulation, dorsal root ganglion, neuropathic pain, complex regional pain syndrome, spinal cord stimulation, chronic pain, implantable neurostimulators, spinal nerve root stimulation.

Long-Term Improvements in Chronic Axial Low Back Pain Patients Without Previous Spinal Surgery: A Cohort Analysis of 10-kHz High-Frequency Spinal Cord Stimulation over 36 Months

Objective

This prospective, open-label study was designed to evaluate the long-term effectiveness of 10-kHz high-frequency spinal cord stimulation (SCS) in the treatment of chronic axial low back pain with no history of spinal surgery.

Methods

Patients with chronic low back pain without previous spinal surgery underwent assessment by a multidisciplinary pain and surgical team to confirm eligibility. After a successful temporary trial of 10-kHz HF-SCS therapy, defined by ≥50% back pain reduction, enrolled subjects underwent permanent system implantation and were followed up for 36 months. Outcome measures consisted of a 100-mm visual analog scale (VAS) for pain intensity, the Oswestry Disability Index (ODI), and a standard measure of health-related quality of life.

Results

Twenty-one patients satisfied the inclusion/exclusion criteria. Following a temporary trial, 20 of 21 (95%) subjects were implanted with a pulse generator, and 17 of 20 reached the 36-month time point. From baseline to 36 months, the average VAS pain intensity decreased from 79 ± 12 mm to 10 ± 12 mm, the average ODI score decreased from 53 ± 13 to 19.8 ± 13, and use of opioids decreased from 18 subjects to two subjects. One subject was deceased, unrelated to the study, one subject was explanted due to loss of effectiveness, and one subject was lost to follow-up.

Conclusions

These results suggest that 10-kHz high-frequency SCS may provide significant, long-term back pain relief, improvement in disability and quality of life, and reduction in opioids for nonsurgical refractory back pain.

Mechanism of Action in Burst Spinal Cord Stimulation: Review and Recent Advances

OBJECTIVE

This is a comprehensive, structured review synthesizing and summarizing the current experimental data and knowledge about the mechanisms of action (MOA) underlying spinal cord stimulation with the burst waveform (as defined by De Ridder) in chronic pain treatment.

METHODS

Multiple database queries and article back-searches were conducted to identify the relevant literature and experimental findings for results integration and interpretation. Data from recent peer-reviewed conference presentations were also included for completeness and to ensure that the most up-to-date scientific information was incorporated. Both human and animal data were targeted in the search to provide a translational approach in understanding the clinical relevance of the basic science findings.

RESULTS/CONCLUSIONS

Burst spinal cord stimulation likely provides pain relief via multiple mechanisms at the level of both the spinal cord and the brain. The specific waveforms and temporal patterns of stimulation both play a role in the responses observed. Differential modulation of neurons in the dorsal horn and dorsal column nuclei are the spinal underpinnings of paresthesia-free analgesia. The burst stimulation pattern also produces different patterns of activation within the brain when compared with tonic stimulation. The latter may have implications for not only the somatic components of chronic pain but also the lateral and affective pathway dimensions as well.

Remote muscle contraction enhances spinal reflexes in multiple lower-limb muscles elicited by transcutaneous spinal cord stimulation

Transcutaneous spinal cord stimulation (tSCS) is a useful technique for the clinical assessment of neurological disorders. However, the characteristics of the spinal cord circuits activated by tSCS are not yet fully understood. In this study, we examined whether remote muscle contraction enhances the spinal reflexes evoked by tSCS in multiple lower-limb muscles. Eight healthy men participated in the current experiment, which required them to grip a dynamometer as fast as possible after the presentation of an auditory cue. Spinal reflexes were evoked in multiple lower-limb muscles with different time intervals (50-400 ms) after the auditory signals. The amplitudes of the spinal reflexes in all the recorded leg muscles significantly increased at 50-250 ms after remote muscle activation onset. This suggests that remote muscle contraction simultaneously facilitates the spinal reflexes in multiple lower-limb muscles. In addition, eight healthy men performed five different tasks (i.e., rest, hand grip, pinch grip, elbow flexion, and shoulder flexion). Compared to control values recorded just before each task, the spinal reflexes evoked at 250 ms after the auditory signals were significantly enhanced by the above tasks except for the rest task. This indicates that such facilitatory effects are also induced by remote muscle contractions in different upper-limb areas. The present results demonstrate the existence of a neural interaction between remote upper-limb muscles and spinal reflex circuits activated by tSCS in multiple lower-limb muscles. The combination of tSCS and remote muscle contraction may be useful for the neurological examination of spinal cord circuits.

Motor Control After Human SCI Through Activation of Muscle Synergies Under Spinal Cord Stimulation

Spinal cord stimulation (SCS) has enabled motor recovery in paraplegics with motor complete spinal cord injury (SCI). However, the physiological mechanisms underlying this recovery are unknown. This paper analyzes muscle synergies in two motor complete SCI patients under SCS during standing and compares them with muscle synergies in healthy subjects, in order to help elucidate the mechanisms that enable motor control through SCS. One challenge is that standard muscle synergy extraction algorithms, such as non-negative matrix factorization (NMF), fail when applied to SCI patients under SCS. We develop a new algorithm-rShiftNMF-to extract muscle synergies in these cases. We find muscle synergies extracted by rShiftNMF are significantly better at interpreting electromyography (EMG) activity, and resulting synergy features are more physiologically meaningful. By analyzing muscle synergies from SCI patients and healthy subjects, we find that: 1) SCI patients rely significantly on muscle synergy activation to generate motor activity; 2) interleaving SCS can selectively activate an additional muscle synergy that is critical to SCI standing; and 3) muscle synergies extracted from SCI patients under SCS differ substantially from those extracted from healthy subjects. We provide evidence that after spinal cord injury, SCS influences motor function through muscle synergy activation.

Transcutaneous spinal direct current stimulation improves locomotor learning in healthy humans

BACKGROUND

Ambulation is an essential aspect of daily living and is often impaired after brain and spinal cord injuries. Despite the implementation of standard neurorehabilitative care, locomotor recovery is often incomplete.

OBJECTIVE

In this randomized, sham-controlled, double-blind, parallel design study, we aimed to determine if anodal transcutaneous spinal direct current stimulation (anodal tsDCS) could improve training effects on locomotion compared to sham (sham tsDCS) in healthy subjects.

METHODS

43 participants underwent a single backwards locomotion training (BLT) session on a reverse treadmill with concurrent anodal (n = 22) or sham (n = 21) tsDCS. The primary outcome measure was speed gain measured 24 h post-training. We hypothesized that anodal tsDCS + BLT would improve training effects on backward locomotor speed compared to sham tsDCS + BLT. A subset of participants (n = 31) returned for two additional training days of either anodal (n = 16) or sham (n = 15) tsDCS and underwent (n = 29) H-reflex testing immediately before, immediately after, and 30 min post-training over three consecutive days.

RESULTS

A single session of anodal tsDCS + BLT elicited greater speed gain at 24 h relative to sham tsDCS + BLT (p = 0.008, two-sample t-test, adjusted for one interim analysis after the initial 12 subjects). Anodal tsDCS + BLT resulted in higher retention of the acquired skill at day 30 relative to sham tsDCS + BLT (p = 0.002) in the absence of significant group differences in online or offline learning over the three training days (p = 0.467 and p = 0.131). BLT resulted in transient down-regulation of H-reflex amplitude (Hmax/Mmax) in both test groups (p < 0.0001). However, the concurrent application of anodal-tsDCS with BLT elicited a longer lasting effect than sham-tsDCS + BLT (p = 0.050).

CONCLUSION

tsDCS improved locomotor skill acquisition and retention in healthy subjects and prolonged the physiological exercise-mediated downregulation of excitability of the alpha motoneuron pool. These results suggest that this strategy is worth exploring in neurorehabilitation of locomotor function.

Supraspinal Mechanisms of Spinal Cord Stimulation for Modulation of Pain: Five Decades of Research and Prospects for the Future

The field of spinal cord stimulation is expanding rapidly, with new waveform paradigms asserting supraspinal sites of action. The scope of treatment applications is also broadening from chronic pain to include cerebral ischemia, dystonia, tremor, multiple sclerosis, Parkinson disease, neuropsychiatric disorders, memory, addiction, cognitive function, and other neurologic diseases. The role of neurostimulation as an alternative strategy to opioids for chronic pain treatment is under robust discussion in both scientific and public forums. An understanding of the supraspinal mechanisms underlying the beneficial effects of spinal cord stimulation will aid in the appropriate application and development of optimal stimulation strategies for modulating pain signaling pathways. In this review, the authors focus on clinical and preclinical studies that indicate the role of supraspinal mechanisms in spinal cord stimulation-induced pain inhibition, and explore directions for future investigations.

Dorsal root ganglion stimulation for chronic pain modulates Aβ-fiber activity but not C-fiber activity: A computational modeling study

OBJECTIVE

The goal of this project was to use computational models to investigate which types of primary sensory neurons are modulated by dorsal root ganglion stimulation (DRGS) to provide pain relief.

METHODS

We modeled DRGS by coupling an anatomical finite element model of a human L5 dorsal root ganglion to biophysical models of primary sensory neurons. We calculated the stimulation amplitude needed to elicit an action potential in each neuron, and examined how DRGS affected sensory neuron activity.

RESULTS

We showed that within clinical ranges of stimulation parameters, DRGS drives the activity of large myelinated Aβ-fibers but does not directly activate small nonmyelinated C-fibers. We also showed that the position of the active and return electrodes and the polarity of the stimulus pulse influence neural activation.

CONCLUSIONS

Our results indicate that DRGS may provide pain relief by activating pain-gating mechanisms in the dorsal horn via repeated activation of large myelinated afferents.

SIGNIFICANCE

Understanding the mechanisms of action of DRGS-induced pain relief may lead to innovations in stimulation technologies that improve patient outcomes.

Computational Study of the Effect of Electrode Polarity on Neural Activation Related to Paresthesia Coverage in Spinal Cord Stimulation Therapy

OBJECTIVE

Using computer simulation, we investigated the effect of electrode polarity on neural activation in spinal cord stimulation and propose a new strategy to maximize the activating area in the dorsal column (DC) and, thus, paresthesia coverage in clinical practice.

MATERIALS AND METHODS

A new three-dimensional spinal cord model at the T10 vertebral level was developed to simulate neural activation induced by the electric field distribution produced by different typical four-contact electrode polarities in single- and dual-lead stimulation. Our approach consisted of the combination of a finite element model of the spinal cord developed in COMSOL Multiphysics and a nerve fiber model implemented in MATLAB. Five evaluation parameters were evaluated, namely, the recruitment ratio, the perception and discomfort thresholds, and the activating area and depth. The results were compared quantitatively.

RESULTS

The dual-guarded cathode presents the maximum activating area and depth in single- and dual-lead stimulation. However, the lowest value of the ratio between the perception threshold in DC and the perception threshold in the dorsal root (DR) is achieved when the guarded cathode is programmed. Although the two versions of bipolar polarity (namely bipolar 1 and bipolar 2) produce higher activating area and depth than the guarded cathode, they are suitable for producing DR stimulation. Similarly, dual-lead stimulation is likely to activate DR fibers because the electrodes are closer to these fibers.

CONCLUSIONS

The results suggest that the activating area in the DC is maximized by using the dual-guarded cathode both in single- and dual-lead stimulation modes. However, DC nerve fibers are preferentially stimulated when the guarded cathode is used. According to these results, the new electrode programming strategy that we propose for clinical practice first uses the dual-guarded cathode, but, if the DR nerve fibers are activated, it then uses guarded cathode polarity.

Electrical spinal cord stimulation must preserve proprioception to enable locomotion in humans with spinal cord injury

Epidural electrical stimulation (EES) of the spinal cord restores locomotion in animal models of spinal cord injury but is less effective in humans. Here we hypothesized that this interspecies discrepancy is due to interference between EES and proprioceptive information in humans. Computational simulations and preclinical and clinical experiments reveal that EES blocks a significant amount of proprioceptive input in humans, but not in rats. This transient deafferentation prevents modulation of reciprocal inhibitory networks involved in locomotion and reduces or abolishes the conscious perception of leg position. Consequently, continuous EES can only facilitate locomotion within a narrow range of stimulation parameters and is unable to provide meaningful locomotor improvements in humans without rehabilitation. Simulations showed that burst stimulation and spatiotemporal stimulation profiles mitigate the cancellation of proprioceptive information, enabling robust control over motor neuron activity. This demonstrates the importance of stimulation protocols that preserve proprioceptive information to facilitate walking with EES.

Anodal Transcutaneous Spinal Direct Current Stimulation (tsDCS) Selectively Inhibits the Synaptic Efficacy of Nociceptive Transmission at Spinal Cord Level

Recently studies have aimed at developing transcutaneous spinal direct current stimulation (tsDCS) as a non-invasive technique to modulate spinal function in humans. Independent studies evaluating its after-effects on nociceptive or non-nociceptive somatosensory responses have reported comparable effects suggesting that tsDCS impairs axonal conduction of both the spino-thalamic and the medial lemniscus tracts. The present study aimed to better understand how tsDCS affects, in humans, the spinal transmission of nociceptive and non-nociceptive somatosensory inputs. We compared the after-effects of anodal low-thoracic, anodal cervical and sham tsDCS on the perception and brain responses elicited by laser stimuli selectively activating Aδ-thermonociceptors of the spinothalamic system and vibrotactile stimuli selectively activating low-threshold Aβ-mechanoreceptors of the lemniscal system, delivered to the hands and feet. Low-thoracic tsDCS selectively and significantly affected the LEP-N2 wave elicited by nociceptive stimulation of the lower limbs, without affecting the LEP-N2 wave elicited by nociceptive stimulation of the upper limbs, and without affecting the SEP-N2 wave elicited by vibrotactile stimulation of either limb. This selective and segmental effect indicates that the neuromodulatory after-effects of tsDCS cannot be explained by anodal blockade of axonal conduction and, instead, are most probably due to a segmental effect on the synaptic efficacy of the local processing and/or transmission of nociceptive inputs in the dorsal horn.

Spinal Cord Stimulation Frequency Influences the Hemodynamic Response in Patients with Disorders of Consciousness

Spinal cord stimulation (SCS) is a promising technique for treating disorders of consciousness (DOCs). However, differences in the spatio-temporal responsiveness of the brain under varied SCS parameters remain unclear. In this pilot study, functional near-infrared spectroscopy was used to measure the hemodynamic responses of 10 DOC patients to different SCS frequencies (5 Hz, 10 Hz, 50 Hz, 70 Hz, and 100 Hz). In the prefrontal cortex, a key area in consciousness circuits, we found significantly increased hemodynamic responses at 70 Hz and 100 Hz, and significantly different hemodynamic responses between 50 Hz and 70 Hz/100 Hz. In addition, the functional connectivity between prefrontal and occipital areas was significantly improved with SCS at 70 Hz. These results demonstrated that SCS modulates the hemodynamic responses and long-range connectivity in a frequency-specific manner (with 70 Hz apparently better), perhaps by improving the cerebral blood volume and information transmission through the reticular formation-thalamus-cortex pathway.

Comparison of the Efficacy of a Gabapentinoid with an Opioid Versus an Opioid Alone in Patients with Spinal Cord Stimulation

BACKGROUND

Combination therapy with a gabapentinoid and an opioid improves the quality of life (QOL) of patients with chronic pain. However, the role of combination therapy in patients with spinal cord stimulation (SCS) has not been evaluated.

OBJECTIVE

Our primary objective was to evaluate the clinical outcomes of combination therapy consisting of a gabapentinoid and an opioid in patients undergoing SCS.

STUDY DESIGN

Retrospective evaluation.

SETTING

Veterans Health Service Medical Center, Seoul, Korea.

METHODS

We retrospectively reviewed 100 military veteran patients who underwent SCS implantation. Forty-eight of 100 patients had been maintained on SCS for 2 years. Patients were divided into 2 groups by analgesic type: group A (opioid only, n = 20) and group B (opioid + gabapentinoids, n = 28). Pre-implantation information included the numeric rating scale (NRS) pain score, quality of life scale (QOLS) score, and oral morphine equivalents (OMEs). Post-implantation data were obtained at 1, 6, 12, and 24 months.

RESULTS

Group B had higher QOLS scores at 1, 6, 12, and 24 months than those of group A (P < 0.05). There were no statistically significant differences in the NRS pain score or OMEs at 1, 6, 12, or 24 months between the 2 groups.

LIMITATION

Retrospective design, relatively short follow up period (2 years).

CONCLUSION

This study indicated that the addition of a gabapentinoid to an opioid is superior to an opioid alone in terms of QOL in military veteran patients with SCS for 2 years. Combination therapy consisting of a gabapentinoid added to an opioid can be a good modality to improve QOL in patients with SCS.

KEY WORDS

Combination, drug therapy, gabapentin, multimodal analgesia, opioid, pain, pregabalin, spinal cord stimulation.

A new minimally invasive technique for lead revision of perc-paddle leads

To report on a less-invasive technique for replacing a broken lead in a spinal cord stimulation (SCS) device that makes use of St. Jude Medical's "Epiducer" device. A 53-year-old woman suffered a loss of stimulation on her internal pulse generator (IPG), which was found to have a broken lead. The broken lead was withdrawn using the Epiducer device with minimal invasiveness and without pain. A new lead was put in place, and successful stimulation using the IPG resumed. Follow-up 3 weeks later showed a well-functioning SCS system. An Epiducer can be used to revise the SCS system in a minimal invasive way without a new puncture. Follow-up study of this technique as well as others for revising an SCS system should be encouraged and used in comparison study.

Comparing the efficacy of targeted spinal cord stimulation (SCS) of the dorsal root ganglion with conventional medical management (CMM) in patients with chronic post-surgical inguinal pain: the SMASHING trial

BACKGROUND

A significant number of patients who undergo a standard inguinal hernia repair or a Pfannenstiel incision develop chronic (> 3 months) post-surgical inguinal pain (PSIP) due to nerve entrapment. If medication or peripheral nerve blocks fail, surgery including neurectomies may offer relief. However, some patients do not respond to any of the currently available remedial treatment modalities. Targeted spinal cord stimulation (SCS) of the dorsal root ganglion (DRG) is a relatively new type of therapy that has a potential to significantly reduce chronic PSIP. The Axium® SCS System (Spinal Modulation Inc., NY, USA) has been shown to be safe and successful in small cohorts of PSIP patients. Aim of this study is to evaluate targeted spinal cord stimulation therapy in patients with PSIP.

METHODS

A prospective, multicentre, randomized controlled trial with optional one-way crossover will assess the efficacy of the Axium® SCS system for the treatment of PSIP. Seventy-eight patients with intractable PSIP following open hernia repair or Pfannenstiel incision who did not respond favorably to previous pain treatment regimens including a neurectomy will be randomized to either an Axium® SCS arm or a control arm receiving only conventional medical management (CMM). Primary outcome is the difference in percentage of subjects with ≥50% pain relief after 6 months using a Numerical Pain Rating Scale (NPRS). Data are collected using a daily pain/sleep diary and a number needed to treat (NNT) analysis is performed. Various secondary outcomes will be collected.

DISCUSSION

Targeted SCS stimulation of the DRG using the Axium® SCS system will possibly offer significant pain reduction in patients with PSIP who are refractory to other treatment modalities.

TRIAL REGISTRATION

The study protocol is registered at the NIH Clinical Trials Registry ( http://clinicaltrials.gov , ClinicalTrials.gov identifier: NCT02349659 ) on January 29, 2015.

Anatomy, Pathophysiology and Interventional Therapies for Chronic Pelvic Pain: A Review

BACKGROUND

Chronic pelvic pain (CPP) represents a group of poorly understood disorders that are often refractory to conventional treatment. Referral to pain management typically occurs later in the continuum of care; as such, many of the injections and nerve blocks commonly prescribed for such patients are potentially limited in efficacy. While neuromodulation is conventionally considered the next algorithmic step in the treatment of chronic pain after injections fail, there is a common perception that neuromodulation is largely ineffective for CPP conditions. However, there is evidence that suggests neuromodulation may in fact be a viable treatment option for this particular patient population when utilized properly.

OBJECTIVES

To provide a basic overview of the pathophysiology of CPP and the relevant neuroanatomy as it pertains to various available treatment options, as well as the techniques and potential targets for neuromodulation.

STUDY DESIGN

Literature review.

SETTING

Private practice, academic and hospital setting.

METHODS

A comprehensive review of the available literature was performed targeting publications focused on CPP and various techniques for utilizing neuromodulation to treat it.

RESULTS

Neuromodulation is an established treatment modalities, however its usefulness as it relates to treating CPP has typically been drawn into question. In this literature review, we discuss the efficacy of various techniques for treating CPP with neuromodulation.

LIMITATIONS

Evidence to support the various treatments, while encouraging, is based on small studies and case series. Large-scale randomized, placebo-controlled clinical trials are warranted to evaluate the clinical efficacy and safety of the different treatments described, particularly neuromodulation.

CONCLUSIONS

In addition to the percutaneous, injection-based treatments described herein, neuromodulation remains a plausible option for recalcitrant cases that fail to respond to more conventional means.

KEY WORDS

Chronic pelvic pain, neuromodulation, spinal cord stimulation, CRPS, complex regional pain syndrome, neuropathic pain.

Effects of Rate on Analgesia in Kilohertz Frequency Spinal Cord Stimulation: Results of the PROCO Randomized Controlled Trial

OBJECTIVE

The PROCO RCT is a multicenter, double-blind, crossover, randomized controlled trial (RCT) that investigated the effects of rate on analgesia in kilohertz frequency (1-10 kHz) spinal cord stimulation (SCS).

MATERIALS AND METHODS

Patients were implanted with SCS systems and underwent an eight-week search to identify the best location ("sweet spot") of stimulation at 10 kHz within the searched region (T8-T11). An electronic diary (e-diary) prompted patients for pain scores three times per day. Patients who responded to 10 kHz per e-diary numeric rating scale (ED-NRS) pain scores proceeded to double-blind rate randomization. Patients received 1, 4, 7, and 10 kHz SCS at the same sweet spot found for 10 kHz in randomized order (four weeks at each frequency). For each frequency, pulse width and amplitude were titrated to optimize therapy.

RESULTS

All frequencies provided equivalent pain relief as measured by ED-NRS (p ≤ 0.002). However, mean charge per second differed across frequencies, with 1 kHz SCS requiring 60-70% less charge than higher frequencies (p ≤ 0.0002).

CONCLUSIONS

The PROCO RCT provides Level I evidence for equivalent pain relief from 1 to 10 kHz with appropriate titration of pulse width and amplitude. 1 kHz required significantly less charge than higher frequencies.

The effect of transcutaneous spinal direct current stimulation on corticospinal excitability in chronic incomplete spinal cord injury

OBJECTIVES

This study investigated the feasibility of modulating bilateral corticospinal excitability with different polarities of transcutaneous spinal direct current stimulation (tsDCS) in chronic, incomplete spinal cord injury (SCI).

METHODS

Six subjects with chronic incomplete SCI (>12 months post injury) participated in this crossover study. Intervention consisted of 3 sessions, separated by at least 1 week, in which each subject received the conditions cathodal, anodal, and sham tsDCS. Stimulation was delivered at 2.5 mA for 20 minutes with the active electrode positioned over the spinous processes of T10-T11 and the reference electrode over left deltoid. To measure the effects of tsDCS on corticospinal excitability, motor evoked potentials (MEPs) from transcranial magnetic stimulation were measured bilaterally from soleus before and after tsDCS.

RESULTS

Five subjects completed all 3 sessions. One subject withdrew after 2 sessions due to complications unrelated to the study. MEPs were measurable in 5 subjects. No significant differences in change of MEP amplitudes were found between the 3 conditions. However, there were trends that indicated laterality of response, particularly with cathodal tsDCS increasing corticospinal excitability contralateral to the reference electrode and decreasing corticospinal excitability ipsilateral to the reference electrode.

CONCLUSION

Corticospinal excitability may be modulated with laterality by tsDCS in individuals with chronic, incomplete SCI. Further research is needed to 1) determine whether different placement of the reference electrode can lead to uniform modulation bilaterally, and 2) reveal whether these alterations in corticospinal excitability can lead to improved movement function in individuals with chronic, incomplete SCI.

Neurostimulation Devices for the Treatment of Neurologic Disorders

Rapid advancements in neurostimulation technologies are providing relief to an unprecedented number of patients affected by debilitating neurologic and psychiatric disorders. Neurostimulation therapies include invasive and noninvasive approaches that involve the application of electrical stimulation to drive neural function within a circuit. This review focuses on established invasive electrical stimulation systems used clinically to induce therapeutic neuromodulation of dysfunctional neural circuitry. These implantable neurostimulation systems target specific deep subcortical, cortical, spinal, cranial, and peripheral nerve structures to modulate neuronal activity, providing therapeutic effects for a myriad of neuropsychiatric disorders. Recent advances in neurotechnologies and neuroimaging, along with an increased understanding of neurocircuitry, are factors contributing to the rapid rise in the use of neurostimulation therapies to treat an increasingly wide range of neurologic and psychiatric disorders. Electrical stimulation technologies are evolving after remaining fairly stagnant for the past 30 years, moving toward potential closed-loop therapeutic control systems with the ability to deliver stimulation with higher spatial resolution to provide continuous customized neuromodulation for optimal clinical outcomes. Even so, there is still much to be learned about disease pathogenesis of these neurodegenerative and psychiatric disorders and the latent mechanisms of neurostimulation that provide therapeutic relief. This review provides an overview of the increasingly common stimulation systems, their clinical indications, and enabling technologies.

Electrical Neuromodulation of the Respiratory System After Spinal Cord Injury

Spinal cord injury (SCI) is a complex and devastating condition characterized by disruption of descending, ascending, and intrinsic spinal circuitry resulting in chronic neurologic deficits. In addition to limb and trunk sensorimotor deficits, SCI can impair autonomic neurocircuitry such as the motor networks that support respiration and cough. High cervical SCI can cause complete respiratory paralysis, and even lower cervical or thoracic lesions commonly result in partial respiratory impairment. Although electrophrenic respiration can restore ventilator-independent breathing in select candidates, only a small subset of affected individuals can benefit from this technology at this moment. Over the past decades, spinal cord stimulation has shown promise for augmentation and recovery of neurologic function including motor control, cough, and breathing. The present review discusses the challenges and potentials of spinal cord stimulation for restoring respiratory function by overcoming some of the limitations of conventional respiratory functional electrical stimulation systems.

Long-term Cost Utility of Spinal Cord Stimulation in Patients with Failed Back Surgery Syndrome

BACKGROUND

Failed back surgery syndrome (FBSS) is a cause of significant morbidity for up to 40% of patients following spine surgery, and is estimated to cost almost $20 billion. Treatment options for these patients currently include conventional medical management (CMM), repeat operation, or spinal cord stimulation (SCS). Much of the published data regarding cost effectiveness of SCS comprise smaller scale randomized controlled trials (RCTs) rather than large databases capturing practices throughout the US. SCS has been shown to have superior outcomes to CMM or repeat spinal operation in several landmark studies, yet there are few large studies examining its long-term economic impact.

OBJECTIVES

This study compares health care utilization for SCS compared to other management in patients with FBSS.

STUDY DESIGN

Retrospective.

SETTING

Inpatient and outpatient sample.

METHODS

Patients with a history of FBSS from 2000 to 2012 were selected. We compared those who received SCS to those who underwent conventional management. A longitudinal analysis was used to model the value of log(cost) in each one year interval using a generalized estimating equations (GEE) model to account for the correlation of the same patient's cost in multiple years. Similarly, a Poisson GEE model with the log link was applied to correlated count outcomes.

RESULTS

We identified 122,827 FBSS patients. Of these, 5,328 underwent SCS implantation (4.34%) and 117,499 underwent conventional management. Total annual costs decreased over time following implantation of the SCS system, with follow-up analysis at 1, 3, 6, and 9 years. The longitudinal GEE model demonstrated that placement of an SCS system was associated with an initial increase in total costs at the time of implantation (cost ratio [CR]: 1.74; 95% confidence interval [CI]: 1.41, 2.15, P < 0.001), however there was a significant and sustained 68% decrease in cost in the year following SCS placement (CR: 0.32; 95% CI: 0.24, 0.42, P < 0.001) compared to CMM. There was also an aggregate time trend that for each additional year after SCS, cost decreased on average 40% percent annually (CR: 0.60; 95% CI: 0.55, 0.65, P < 0.001), with follow-up up to 1, 3, 6, and 9 years post-procedure.

LIMITATIONS

Costs are not correlated with patient outcomes, patients are not stratified in terms of complexity of prior back surgery, as well as inherent limitations of a retrospective analysis.

CONCLUSIONS

We found that from 2000 to 2012, only 4.3% of patients across the United States with FBSS were treated with SCS. Long-term total annual costs for these patients were significantly reduced compared to patients with conventional management. Although implantation of an SCS system results in a short-term increase in costs at one year, the subsequent annual cumulative costs were significantly decreased long-term in the following 9 years after implantation. This study combines the largest group of FBSS patients studied to date along with the longest follow-up interval ever analyzed. Since SCS has repeatedly been shown to have superior efficacy to CMM in randomized clinical trials, the current study demonstrating improved long-term health economics at 1, 3, 6, and 9 years supports the long-term cost utility of SCS in the treatment of FBSS patients. Key words: Failed back surgery syndrome, spinal cord stimulation, back pain, leg pain, neuromodulation, FBSS, SCS.

Motor cortex and spinal cord neuromodulation promote corticospinal tract axonal outgrowth and motor recovery after cervical contusion spinal cord injury

Cervical injuries are the most common form of SCI. In this study, we used a neuromodulatory approach to promote skilled movement recovery and repair of the corticospinal tract (CST) after a moderately severe C4 midline contusion in adult rats. We used bilateral epidural intermittent theta burst (iTBS) electrical stimulation of motor cortex to promote CST axonal sprouting and cathodal trans-spinal direct current stimulation (tsDCS) to enhance spinal cord activation to motor cortex stimulation after injury. We used Finite Element Method (FEM) modeling to direct tsDCS to the cervical enlargement. Combined iTBS-tsDCS was delivered for 30min daily for 10days. We compared the effect of stimulation on performance in the horizontal ladder and the Irvine Beattie and Bresnahan forepaw manipulation tasks and CST axonal sprouting in injury-only and injury+stimulation animals. The contusion eliminated the dorsal CST in all animals. tsDCS significantly enhanced motor cortex evoked responses after C4 injury. Using this combined spinal-M1 neuromodulatory approach, we found significant recovery of skilled locomotion and forepaw manipulation skills compared with injury-only controls. The spared CST axons caudal to the lesion in both animal groups derived mostly from lateral CST axons that populated the contralateral intermediate zone. Stimulation enhanced injury-dependent CST axonal outgrowth below and above the level of the injury. This dual neuromodulatory approach produced partial recovery of skilled motor behaviors that normally require integration of posture, upper limb sensory information, and intent for performance. We propose that the motor systems use these new CST projections to control movements better after injury.

Efficacy of Short-Term Spinal Cord Stimulation in Acute/Subacute Zoster-Related Pain: A Retrospective Study

BACKGROUND

Postherpetic neuralgia (PHN) is a refractory condition that impairs the patient's quality of life (QoL), it develops secondary to herpes zoster infection. Therefore, it's important to prevent the transition of acute/subacute zoster-related pain to PHN. Despite of numerous studies, the optimal intervention that reduces PHN incidence is still unknown.

OBJECTIVE

We evaluate the efficacy of short-term spinal cord stimulation (stSCS) in patients with refractory acute/subacute zoster-related pain.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary referral center/teaching hospital.

METHODS

A total of 46 patients who presented with acute/subacute zoster-related pain, and had previously failed conventional therapies, underwent stSCS treatment. Visual analog scale (VAS), Short Form Health Survey 12 items (SF-12), and analgesic consumptions were recorded before stSCS, post-stSCS, 2 weeks, and 1, 3, 6, 9, and 12 months after stimulation.

RESULTS

The VAS scores at post-stSCS, 2 weeks, and 1, 3, 6, 9, and 12 months after stSCS treatment were significantly decreased compared with the baseline score (P < 0.001). Thirty-two patients (69.6%, 32/46) achieved the minimal clinically important difference (MCID), including 18 patients (39.1%, 18/46) who achieved complete pain relief (VASless than orequal to2). During the follow-up period, the efficacy of stSCS didn't decrease and VAS scores were declining. Similarly, SF-12 scores and analgesic consumptions improved after stSCS treatment. The efficacy of stSCS did not differ significantly among patients with different durations of acute/subacute zoster-related pain starting from the onset of rash. No serious adverse effects were observed in the entire follow-up period.

LIMITATIONS

This study was not a randomized prospective controlled study. We did not compare the outcomes with patients presenting with mild or moderate pain, and did not compare the efficacy of stSCS treatment with conventional therapies.

CONCLUSIONS

stSCS is a safe, effective, and less invasive analgesic method for patients with refractory acute/subacute zoster-related pain.

KEY WORDS

Herpes zoster, zoster-related pain, postherpetic neuralgia, spinal cord stimulation, VAS.

The effects of cervical transcutaneous spinal direct current stimulation on motor pathways supplying the upper limb in humans

Non-invasive, weak direct current stimulation can induce changes in excitability of underlying neural tissue. Many studies have used transcranial direct current stimulation to induce changes in the brain, however more recently a number of studies have used transcutaneous spinal direct current stimulation to induce changes in the spinal cord. This study further characterises the effects following cervical transcutaneous spinal direct current stimulation on motor pathways supplying the upper limb. In Study 1, on two separate days, participants (n = 12, 5 F) received 20 minutes of either real or sham direct current stimulation at 3 mA through electrodes placed in an anterior-posterior configuration over the neck (anode anterior). Biceps brachii, flexor carpi radialis and first dorsal interosseous responses to transcranial magnetic stimulation (motor evoked potentials) and cervicomedullary stimulation (cervicomedullary motor evoked potentials) were measured before and after real or sham stimulation. In Study 2, on two separate days, participants (n = 12, 7 F) received either real or sham direct current stimulation in the same way as for Study 1. Before and after real or sham stimulation, median nerve stimulation elicited M waves and H reflexes in the flexor carpi radialis. H-reflex recruitment curves and homosynaptic depression of the H reflex were assessed. Results show that the effects of real and sham direct current stimulation did not differ for motor evoked potentials or cervicomedullary motor evoked potentials for any muscle, nor for H-reflex recruitment curve parameters or homosynaptic depression. Cervical transcutaneous spinal direct current stimulation with the parameters described here does not modify motor responses to corticospinal stimulation nor does it modify H reflexes of the upper limb. These results are important for the emerging field of transcutaneous spinal direct current stimulation.

Electrical neuromodulation of the cervical spinal cord facilitates forelimb skilled function recovery in spinal cord injured rats

Enabling motor control by epidural electrical stimulation of the spinal cord is a promising therapeutic technique for the recovery of motor function after a spinal cord injury (SCI). Although epidural electrical stimulation has resulted in improvement in hindlimb motor function, it is unknown whether it has any therapeutic benefit for improving forelimb fine motor function after a cervical SCI. We tested whether trains of pulses delivered at spinal cord segments C6 and C8 would facilitate the recovery of forelimb fine motor control after a cervical SCI in rats. Rats were trained to reach and grasp sugar pellets. Immediately after a dorsal funiculus crush at C4, the rats showed significant deficits in forelimb fine motor control. The rats were tested to reach and grasp with and without cervical epidural stimulation for 10weeks post-injury. To determine the best stimulation parameters to activate the cervical spinal networks involved in forelimb motor function, monopolar and bipolar currents were delivered at varying frequencies (20, 40, and 60Hz) concomitant with the reaching and grasping task. We found that cervical epidural stimulation increased reaching and grasping success rates compared to the no stimulation condition. Bipolar stimulation (C6- C8+ and C6+ C8-) produced the largest spinal motor-evoked potentials (sMEPs) and resulted in higher reaching and grasping success rates compared with monopolar stimulation (C6- Ref+ and C8- Ref+). Forelimb performance was similar when tested at stimulation frequencies of 20, 40, and 60Hz. We also found that the EMG activity in most forelimb muscles as well as the co-activation between flexor and extensor muscles increased post-injury. With epidural stimulation, however, this trend was reversed indicating that cervical epidural spinal cord stimulation has therapeutic potential for rehabilitation after a cervical SCI.

Epidural Spinal Stimulation to Improve Bladder, Bowel, and Sexual Function in Individuals With Spinal Cord Injuries: A Framework for Clinical Research

While some recent studies that apply epidural spinal cord stimulation (SCS) have demonstrated a breakthrough in improvement of the health and quality of the life of persons with spinal cord injury (SCI), the numbers of people who have received SCS are small. This is in sharp contrast to the thousands of persons worldwide living with SCI who have no practical recourse or hope of recovery of lost functions. Thus, the vision is to understand the full potential of this new intervention and to determine if it is safe and effective in a larger cohort, and if it is scalable so that it can be made available to all those who might benefit. To achieve this vision, the National Institute of Biomedical Imaging and Bioengineering called for and organized a consortium of multiple stakeholder groups: foundations addressing paralysis, federal and public agencies, industrial partners, academicians, and researchers, all interested in the same goal. Based on input from consortium participants, we have reasoned that a first step is to define a scalable SCS approach that is effective in restoring lost autonomic physiology, specifically bladder, bowel, and sexual function. These functions are most critical for improving the quality of life of persons living with SCI. This report outlines a framework for conducting the research needed to define such an effective SCS procedure that might seek Food and Drug Administration approval and be implemented at the population level.

Complications of Spinal Cord Stimulation and Peripheral Nerve Stimulation Techniques: A Review of the Literature

OBJECTIVE

Spinal cord and peripheral neurostimulation techniques have been practiced since 1967 for the relief of pain, and some techniques are also used for improvement in organ function. Neuromodulation has recognized complications, although very rarely do these cause long-term morbidity. The aim of this article is to present a review of complications observed in patients treated with neurostimulation techniques.

METHODS

A review of the major recent publications in the literature on the subjects of spinal cord, occipital, sacral, and peripheral nerve field stimulation was conducted.

RESULTS

The incidence of complications reported varies from 30% to 40% of patients affected by one or more complications. Adverse events can be subdivided into hardware-related complications and biological complications. The commonest hardware-related complication is lead migration. Other lead related complications such as failure or fracture have also been reported. Common biological complications include infection and pain over the implant. Serious biological complications such as dural puncture headache and neurological damage are rarely observed.

CONCLUSIONS

Spinal cord and peripheral neurostimulation techniques are safe and reversible therapies. Hardware-related complications are more commonly observed than biological complications. Serious adverse events such as neurological damage are rare.

[The influence of non-invasive electrical stimulation of the spinal cord on the locomotor function of patients presenting with movement disorders of central genesis]

AIM

The objective of the present study was to evaluate the influence of non-invasive (transcutaneous) electrical spinal cord stimulation on the locomotor function of the patients suffering from movement disorders.

PATIENTS AND METHODS

The study involved 10 patients of both sexes at the age from 32 to 70 years (including 40% of men and 60% of women) presenting with the compromised locomotor function of varying severity associated with the disturbances of cerebral blood circulation caused either by an injury to the brain and spinal cord or by stroke. The transcutaneous electrical spinal cord stimulation was applied using different frequency regimes with the placement of the electrodes in the projection onto the region of TXI-TXII vertebrae. The active factors were bipolar electrical stimuli 0.5 ms in duration; the current strength was chosen for each patient on an individual basis taking into consideration its threshold level. Electromyograms and evoked motor responses of selected muscles, viz. m. rectus femoris, m.biceps femoris, m. tibialis anterior, and m.gastrocnemius were recorded with the use of the 'Neuro-MVP-8 eight-channel electromyography' ('Neurosoft', Russia).

RESULTS

The data obtained give evidence that the stimulation of the spinal cord with a frequency of 1 Hz induces reflectory responses with monosynaptic and polysynaptic components in the muscles of the lower extremities, with the thresholds of these responses being significantly higher in the patients presenting with serious neurological problems. Stimulation with the frequencies of 5 and 30 Hz caused in the patients with paresis the involuntary movement of the legs the characteristics of which were similar to those of the locomotor movements.

CONCLUSION

It has been demonstrated that the application of transcutaneous electrical spinal cord stimulation leads to increased excitability of the lumbar spinal neural structures of the patients. The study has shown the possibility of regulation of the locomotor functions in the patients presenting with movement disorders of central genesis by means of non-invasive electrical stimulation of the spinal cord.

Spinal Cord Stimulation: An Alternative Concept of Rehabilitation?

BACKGROUND

Chronic low back and leg pain is a disabling condition, affecting, in most cases, older patients with congenital or acquired spinal stenosis or patients with failed back surgery syndrome. Spinal cord stimulation has been introduced as an effective therapeutic option for those patients who have previously been operated without significant clinical benefits, or for all those patients who are ineligible for traditional surgery.

METHODS

We report our experience with ten patients treated with spinal cord stimulation plus medication and physical therapy between November 2014 and September 2015. Inclusion criteria were: previous surgical treatments for lumbar stenosis and metameric instability and persistent or ingravescent disabling low back and leg pain, with a mean duration of symptoms of at least 18 months. A visual analog scale (VAS) was employed for back and leg pain, and the Oswestry Disability Index (ODI) score was determined, and findings were analyzed after 6 months.

FINDINGS

No intra- or postoperative complication was recorded. The mean VAS score for back pain decreased from 7.5 to 2.9, while leg VAS decreased from 8.2 to 3.0. Analysis of ODI values showed evident improvement in daily life activities, ranging from a median value of 75.7% to 32.7 % after the stimulation.

CONCLUSION

Spinal cord stimulation has a recognized impact on the pain and on the quality of life of patients with failed back surgery syndrome.

The proposed use of cervical spinal cord stimulation for the treatment and prevention of cognitive decline in dementias and neurodegenerative disorders

Cervical spinal cord stimulation is a well-established treatment for intractable neuropathic upper extremity pain. More than 20years ago it was demonstrated that cervical spinal cord stimulation could engender an increase in cerebral blood flow. Cerebral blood flow has been shown to be decreased in many patients with dementia and in various neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. Furthermore, there is evidence that reduced cerebral blood flow worsens neurodegenerative disease and may also predict which patients progress from mild cognitive impairment to full blown Alzheimer's disease. Thus, the identification of decreased cerebral blood flow in patients with early cognitive problems may offer clinicians a window of opportunity to intervene and prevent further brain damage. Further evidence that supports augmenting cerebral blood flow as an effective strategy for preventing and treating cognitive brain dysfunction comes from experimental studies with omental transposition. The author proposes cervical spinal cord stimulation as a titratable, programmable extracranial neuromodulation technique to increase cerebral blood flow for the purposes of improving cognitive function and preventing cognitive deterioration in patients with dementias and neurodegenerative disorders.

Epidural Stimulation of Rat Spinal Cord at Lumbosacral Segment Using a Surface Electrode: A Computer Simulation Study

Clinical research indicates that the epidural spinal cord stimulation (ESCS) at lumbosacral segment has shown potential for promoting locomotor recovery in patients with incomplete spinal cord injury. However, the underlying neural mechanism needs to be determined by animal experiments. In order to refine experimental protocols, we used a finite element simulation to investigate the activation of nerve fibers in a rat spinal cord model. Our model is composed of a volume conductor model from L1 to S2 spinal segments and the McIntyre-Richard-Grill axon model, which is used to investigate the threshold of selected spinal fibers with different diameters at varied locations and predict the neural responses of any target fibers with bipolar electrode configuration. Mathematical modeling suggests that the electrode-fiber distance may play an important role in the recruitment of nerve fibers, whereas longer pulse width predicted greater activity of spinal root fibers and dorsal column fibers, as well as may exert an effective influence on the motor system by the ability to increase and even "steer" spatial selectivity with deeper penetration into the dorsal columns. The spikes were initiated at sites along the nerve fibers depending on which component was closest to the cathode among the longitudinal part of the fiber, its entrance into spinal cord, or strong bending at the entry. Our simulation results show good agreement with the previous findings from animal studies. It is concluded that the computational ESCS model is a valuable tool to obtain a better insight into the immediately evoked electrophysiological phenomena in animal models, and provides further guidelines for conducting animal experiments to enhance the exploration of basic neural mechanisms.

[SCS as a treatment option for failed back surgery syndrome]

Unfortunately, 10-40 % of patients still experience pain after spinal surgery. There are many reasons for the patients' complaints. If no identifiable cause, such as a recurrent disc herniation, is visible, this is referred to as failed back surgery syndrome. However, this definition includes a variety of possible underlying causes of the pain, which result in just as many different therapeutic approaches. In addition to pharmacological, behavioral and physical therapy, also neuromodulation techniques can be offered; the best known method is spinal cord stimulation (SCS). The following article describes evidence-based studies with regard to the beneficial treatment of failed back surgery syndrome with conventional tonic SCS and new developments in spinal cord stimulation addressing the treatment of chronic refractory back pain.

Pain Relief in CRPS-II after Spinal Cord and Motor Cortex Simultaneous Dual Stimulation

We describe a case of a 30-year-old woman who suffered a traumatic injury of the right brachial plexus, developing severe complex regional pain syndrome type II (CRPS-II). After clinical treatment failure, spinal cord stimulation (SCS) was indicated with initial positive pain control. However, after 2 years her pain progressively returned to almost baseline intensity before SCS. Additional motor cortex electrode implant was then proposed as a rescue therapy and connected to the same pulse generator. This method allowed simultaneous stimulation of the motor cortex and SCS in cycling mode with independent stimulation parameters in each site. At 2 years follow-up, the patient reported sustained improvement in pain with dual stimulation, reduction of painful crises, and improvement in quality of life. The encouraging results in this case suggests that this can be an option as add-on therapy over SCS as a possible rescue therapy in the management of CRPS-II. However, comparative studies must be performed in order to determine the effectiveness of this therapy.

KEY WORDS

Chronic neuropathic pain, Complex regional pain syndrome Type II, brachial plexus injury, motor cortex stimulation, spinal cord stimulation.

[Evaluation of motor neuron excitability in lumbosacral spinal cord: Transcutaneous spinal cord stimulation as compared to H-reflex]

Multisegmental muscle responses (MMR) are reflexes in the leg muscles evoked by transcutaneous electrical spinal cord stimulation over the Th11–Th12 vertebrae. We have used MMR to evaluate the excitability of lumbosacral motor neurons in individuals suffering lower paraplegia. Ten individuals were tested using H-reflexes and MMR bilaterally before (n 0 = 20) and during 4-weeks course of rehabilitation (n=76). The H-reflex and MMR of m. gastrocnemius lateralis were obtained in: 15 and 13 cases out of 20, respectively. Both reflexes were recorded in 11 and were absent in 3 cases, matched up to 70% of recordings. In dynamic, the both methods were 100% reproducible and the responses’ amplitude varied in similar directions in 67% of records. The data confirm the validity and reproducibility of the MMR for evaluation of the motor neurons excitability in lumbosacral cord. The H-reflex magnitude shows moderate correlation with MMR in m. gastrocnemius lateralis (r = 0.59, p < 0.001), and low correlation with MMR in mm. rectus femoris, biceps femoris, and tibialis anterior (r < 0.40, p < 0.001). These findings do not allow extrapolate the results from the H-reflex measurement on the state of lumbosacral cord. At the same time, measurements of the MMR allow estimate simultaneously the excitability of motor pools innervating several muscle groups. This makes advantageous to assess the functional state of the motor neurons in the lumbosacral spinal cord for clinical and experimental studies, including the spinal cord damage.

High Frequency Spinal Cord Stimulation at 10 kHz for the Treatment of Chronic Pain: 6-Month Australian Clinical Experience

BACKGROUND

High frequency spinal cord stimulation at 10 kHz (HF10 therapy) represents a prominent advance in spinal cord stimulation (SCS) therapy, having demonstrated enhanced efficacy in patients with back and leg pain and pain relief without paresthesia that is sustained at 24 months post implant.

OBJECTIVE

To report on the effectiveness HF10 SCS therapy for a wide range of intractable pain conditions in clinical practice.

STUDY DESIGN

Retrospective investigation of 256 patients who trialed HF10 SCS for chronic intractable pain of various etiologies.

SETTING

Three Australian pain clinics.

METHODS

Two hundred fifty-six patients trialed HF10 SCS with view of a permanent implant if successful. Pain distributions included back + leg, back only, head ± neck, and neck ± arm/shoulder. About 30% of patients had previously failed traditional low-frequency paresthesia-based stimulation, while the remaining cohort were either highly refractory to treatment or not recommended by the pain physician for traditional SCS. Pain scores (numerical pain rating scale - NPRS) and functional outcome measures (Oswestry Disability Index - ODI; and activity tolerance times) were assessed at baseline, post-trial, and at 3 and 6 months post-implant as available in the medical records.

RESULTS

Of the 256 patients, 189 (73%) reported a positive trial and were implanted. Patients with back + leg pain demonstrated the highest trial success rate (81%). A mean reduction in pain, among those for whom data were available, of 50% was sustained up to 6 months post-implant across the entire patient population. Sixty-eight percent of patients who failed traditional SCS reported a positive trial and mean pain relief at 6 months was 49% (P < 0.001). An 8.6 point reduction in ODI (21%) at 6 months and improved sitting, standing, and walking tolerances were also reported.

LIMITATIONS

As data was collected retrospectively, missing data points were unavoidable; this was primarily due to inconsistent data collection and patients being lost to follow-up. Patient populations were diverse and a control group was not appropriate in this setting.

CONCLUSIONS

These retrospective results demonstrate a significant advancement for patients suffering with chronic intractable pain and are consistent with recently published clinical results for HF10 SCS. HF10 SCS appears to be a viable, paresthesia-free alternative to traditional SCS, with high trial success rates, demonstrated effectiveness in a range of pain distributions including those typically difficult to treat with traditional SCS, and the possibility to restore pain control in patients who have previously failed traditional SCS.

KEY WORDS

Spinal cord stimulation, high frequency stimulation, HF10, paresthesia-free stimulation, back pain, leg pain, cervical pain, neuromodulation.

Targeting Lumbar Spinal Neural Circuitry by Epidural Stimulation to Restore Motor Function After Spinal Cord Injury

Epidural spinal cord stimulation has a long history of application for improving motor control in spinal cord injury. This review focuses on its resurgence following the progress made in understanding the underlying neurophysiological mechanisms and on recent reports of its augmentative effects upon otherwise subfunctional volitional motor control. Early work revealed that the spinal circuitry involved in lower-limb motor control can be accessed by stimulating through electrodes placed epidurally over the posterior aspect of the lumbar spinal cord below a paralyzing injury. Current understanding is that such stimulation activates large-to-medium-diameter sensory fibers within the posterior roots. Those fibers then trans-synaptically activate various spinal reflex circuits and plurisegmentally organized interneuronal networks that control more complex contraction and relaxation patterns involving multiple muscles. The induced change in responsiveness of this spinal motor circuitry to any residual supraspinal input via clinically silent translesional neural connections that have survived the injury may be a likely explanation for rudimentary volitional control enabled by epidural stimulation in otherwise paralyzed muscles. Technological developments that allow dynamic control of stimulation parameters and the potential for activity-dependent beneficial plasticity may further unveil the remarkable capacity of spinal motor processing that remains even after severe spinal cord injuries.

Combined Spinal Cord Stimulation and Peripheral Nerve Stimulation for Brachial Plexopathy: A Case Report

Brachial plexopathy usually results from an iatrogenic brachial plexus injury and can sometimes cause severe chronic pain and disability. There are a number of possible treatments for this condition, including medication, physical therapy, nerve blocks, and neuromodulation, but they are not always successful. Recently, combined spinal cord stimulation (SCS) and peripheral nerve stimulation (PNS) have been tried for various chronic pain diseases because of their different mechanisms of action.Here, we describe the case of a 54-year-old man who was diagnosed with brachial plexopathy 8 years ago. He underwent video-assisted thoracoscopic surgery to remove a superior mediastinal mass. However, his brachial plexus was damaged during the surgery. Although he had received various treatments, the pain did not improve. For the management of intractable severe pain, he underwent SCS 2 years ago, which initially reduced his pain from numeric rating scale (NRS) 10/10 to NRS 4 - 5/10, but the pain then gradually increased, reaching NRS 8/10, 6 months ago. At that time, he was refractory to other treatments, and we therefore applied PNS in combination with SCS. The PNS electrode was positioned on the radial nerve under ultrasound guidance. After combined PNS and SCS, his background pain disappeared, although a breakthrough pain (NRS 3 - 4/10) was caused intermittently by light touch. Furthermore, the patient's need for analgesics decreased, and he was satisfied with the outcome of this combined treatment. We concluded that combined SCS and PNS is a very useful treatment modality, which can stimulate the target nerve both directly and indirectly, and hence, relieve pain from brachial plexopathy.

Spinal Cord Stimulation for Complex Regional Pain Syndrome: A Case Study of a Pregnant Female

BACKGROUND

Spinal cord stimulation (SCS) is a form of neuromodulation, used to treat chronic neuropathic pain refractory to conventional medical management. Spinal cord stimulators are treatment options when intractable chronic pain has not responded to more conventional treatment modalities. Currently, the use of SCS is contraindicated in pregnancy. Nevertheless, many SCS/neuromodulation recipients are women of child bearing age who may become pregnant. There are no published reports that focus on the possible side effects of SCS or neuromodulation therapy on human fertility, fetal development, pregnancy, delivery, or lactation.

OBJECTIVES

The purpose of this current report is to present a case study on the use of SCS/neuromodulation during pregnancy.

STUDY DESIGN

Presentation of the case of a 24 year old female who became pregnant after receiving an SCS implantation for pain control secondary to complex regional pain syndrome (CRPS). The SCS was in use at the time of conception but deactivated when patient became aware of her pregnancy and intermittently reactivated for five minute intervals throughout the entire pregnancy.

RESULTS

Currently very little documented evidence is available regarding the safety of using a SCS/neuromodulator during pregnancy; therefore its use during pregnancy is contraindicated. Available literature suggests that, women who have chosen to keep the SCS/neuromodulator activated during pregnancy have delivered healthy babies without any life threatening complications.

LIMITATIONS

Case presentations do not provide conclusive evidence of treatment effectiveness. This data is only preliminary and future studies should be used to assess outcomes and measures to provide quantification of the SCS implantation during pregnancy.

CONCLUSIONS

Women of child bearing age who are recipients of SCS/neuromodulation implantation should be informed of the limited knowledge available regarding the impact of SCS/neuromodulation use during pregnancy. For current recipients, decisions about ongoing use during pregnancy should be an individual decision based on the potential risks and benefits.

Advanced Innovations for Pain

Chronic pain represents one of the most important public health problems in terms of both the number of patients afflicted and health care costs. Most patients with chronic pain are treated with medications as the mainstay of therapy, and yet most medically treated patients continue to report ongoing pain. Additionally, adverse effects from pain medications represent a major challenge for clinicians and patients. Spinal cord stimulation and intrathecal drug delivery systems are well-established techniques that have been utilized for over 25 years. Intrathecal drug delivery systems have proven efficacy for a wide variety of intractable pain conditions and fewer adverse effects than systemic medical therapy in patients with refractory cancer-related pain. Spinal cord stimulation is cost-effective and provides improved pain control compared with medical therapy in patients with a variety of refractory pain conditions including complex regional pain syndrome, painful diabetic neuropathy, and chronic radiculopathy. Patients who have intractable pain that has not responded to reasonable attempts at conservative pain care measures should be referred to a qualified interventional pain specialist to determine candidacy for the procedures discussed in this article.

Effectiveness of Spinal Cord Stimulation in Chronic Spinal Pain: A Systematic Review

BACKGROUND

Chronic neuropathic pain has been recognized as contributing to a significant proportion of chronic pain globally. Among these, spinal pain is of significance with failed back surgery syndrome (FBSS), generating considerable expense for the health care systems with increasing prevalence and health impact.

OBJECTIVE

To assess the role and effectiveness of spinal cord stimulation (SCS) in chronic spinal pain.

STUDY DESIGN

A systematic review of randomized controlled trials (RCTs) of SCS in chronic spinal pain.

METHODS

The available literature on SCS was reviewed. The quality assessment criteria utilized were Cochrane review criteria to assess sources of risk of bias and Interventional Pain Management Techniques - Quality Appraisal of Reliability and Risk of Bias Assessment (IPM - QRB) criteria for randomized trials.The level of evidence was based on a best evidence synthesis with modified grading of qualitative evidence from Level I to Level V.Data sources included relevant literature published from 1966 through March 2015 that were identified through searches of PubMed and EMBASE, manual searches of the bibliographies of known primary and review articles, and all other sources.

OUTCOME MEASURES

RCTs of efficacy with a minimum 12-month follow-up were considered for inclusion. For trials of adaptive stimulation, high frequency stimulation, and burst stimulation, shorter follow-up periods were considered.

RESULTS

Results showed 6 RCTs with 3 efficacy trials and 3 stimulation trials. There were also 2 cost effectiveness studies available. Based on a best evidence synthesis with 3 high quality RCTs, the evidence of efficacy for SCS in lumbar FBSS is Level I to II. The evidence for high frequency stimulation based on one high quality RCT is Level II to III. Based on a lack of high quality studies demonstrating the efficacy of adaptive stimulation or burst stimulation, evidence is limited for these 2 modalities.

LIMITATIONS

The limitations of this systematic review continue to require future studies illustrating effectiveness and also the superiority of high frequency stimulation and potentially burst stimulation.

CONCLUSION

There is significant (Level I to II) evidence of the efficacy of spinal cord stimulation in lumbar FBSS; whereas, there is moderate (Level II to III) evidence for high frequency stimulation; there is limited evidence for adaptive stimulation and burst stimulation.

Modeling dermatome selectivity of single-and multiple-current source spinal cord stimulation systems

A recently published computational modeling study of spinal cord stimulation (SCS) predicted that a multiple current source (MCS) system could generate a greater number of central points of stimulation in the dorsal column (DC) than a single current source (1 CS) system. However, the clinical relevance of this finding has not been established. The objective of this work was to compare the dermatomal zone selectivity of MCS and 1 CS systems. A finite element method (FEM) model was built with a representation of the spinal cord anatomy and a 2 × 8 paddle electrode array. Using a contact configuration with two aligned tripoles, the FEM model was used to solve for DC field potentials across incremental changes in current between the two cathodes, modeling the MCS and 1 CS systems. The activation regions within the DC were determined by coupling the FEM output to a biophysical nerve fiber model, and coverage was mapped to dermatomal zones. Results showed marginal differences in activated dermatomal zones between 1 CS and MCS systems. This indicates that a MCS system may not provide incremental therapeutic benefit as suggested in prior analysis.

Hypodermis Tension Loop: A New Preventative Measure for Lead Migration in the Morbidly Obese

Electrode migration/displacement is reported to be the most common complication of spinal cord stimulator (SCS) implantation, with the literature reporting incidences from 13.2% to 22.6%. There have been numerous publications describing techniques preventing lead migration, with most involving tying leads to skin and fascia for trial and permanent leads, respectively. However, few have addressed how to prevent migration in the case of hypermobile tissue seen in the morbidly obese. We describe the creation of subcutaneous tension loops to prevent lead migration.